In exhaust systems of internal combustion engines, it may be necessary for various reasons to spray a liquid educt into the exhaust stream. For example, fuel may be injected into the exhaust stream upstream from an oxidation catalyst to trigger an exothermic combustion reaction on a downstream oxidation catalyst. Likewise, a reducing agent such as ammonia, for example, may be sprayed into the exhaust stream to reduce nitrose gases entrained by the exhaust gas in a downstream SCR catalytic converter. Instead of ammonia, urea and/or an aqueous urea solution may also be injected into the exhaust stream. Then ammonia and water are formed from the aqueous urea solution by a hydrolysis reaction. Furthermore, a fuel or another suitable reducing agent may be injected into the exhaust stream upstream from an NOX storage catalyst to regenerate the NOX storage catalyst.
To improve and/or enable the efficiency of the educt injected in liquid form into the exhaust line, extensive evaporation is as desirable as is thorough mixing with the exhaust gas to thereby achieve the most homogeneous possible exhaust-gas-educt mixture. To do so, the exhaust system may be equipped with a mixing and/or evaporation installation arranged in the exhaust line downstream from the injection device.
Depending on the injection equipment used, the educt may be introduced in the form of a liquid jet which widens in a conical pattern. At low engine loads and exhaust gas temperatures, low exhaust gas temperatures and low velocities of flow prevail. The liquid jet may subsequently strike a corresponding structure of the mixing and/or evaporation installation. Depending on the design of the mixing and/or evaporation installation, the liquid jet may penetrate unhindered at least partially through the respective structure of the mixing and/or evaporation installation and then reach the exhaust gas treatment device in liquid form, in which device the sprayed liquid should arrive only in the form of the most homogeneous possible gas mixture. The result would be a reduced efficiency and the risk of damage.